The Mystery of the Siberian Pinkie: When Classification goes Wrong

Biological classification is often misunderstood and misused in the scientific literature and especially in the media:

“... birds are dinosaurs” (New York Times, 2010).

“Humans are apes” (Dawkins, 2010 in The Australian).

“Scientists have identified a previously unknown type of ancient human through analysis of DNA from a finger bone unearthed in a Siberian cave” (BBC News Online).

These slogans, popular with the public, are completely misinformed and provide inaccurate information about biological classification. Let’s start with birds are dinosaurs.

The slogan assumes we know something about the classification of dinosaurs, namely that they include birds. This assumption derives from a cladogram that shows that some dinosaurs (feathered therapods) are more closely related to birds than they are to other dinosaurs (see Gauither et al., 1998).

Moreover, birds are diagnosed as any amniote that possesses feathers, meaning that therapods are birds. The slogan then should instead read “some dinosaurs are birds”. This then begs the question “what are dinosaurs?”

The phrase “Humans are apes” has been used quite often as a slogan, most notably by Richard Dawkins. Like the dinosaur bird example, it assumes that we know something about human classification. In fact, the term ‘ape’ refers to:

“... any of two families (Pongidae and Hylobatidae) of large tailless semi-erect primates (as the chimpanzee, gorilla, orangutan, or gibbon) ...” (Merriam-Webster Online Dictionary, 2010).

Humans on the other hand belong to the Hominidae. In classification and in common usage, we are hominids and not apes. So why the confusion?

Many scientists misuse existing terms in classification to make assumptions about evolution. Since evolution and classification are two separate issues, there is a degree of confusion. The slogan “humans are apes” is supposed to infer that humans evolved from apes or both apes and humans evolved from something else. In classification, this slogan is meaningless, unless it is meant to say that humans are members of either pongidae and hylobatidae. The same misuse of classification can be seen in a recent report of a newly discovered hominid from Siberia. The report by Krause et al (2010) states:

“DNA sequence retrieved from a bone [the distal manual phalanx of the fifth digit, or the 'pinkie'] excavated in 2008 in Denisova Cave in the Altai Mountains in southern Siberia. It represents a hitherto unknown type of hominin mtDNA that shares a common ancestor with anatomically modern human and Neanderthal mtDNAs about 1.0 million years ago (Krause et al., 2010).

mtDNA is not used in taxonomy to diagnose new species. Moreover the variability in mtDNA has been found to be high between individuals (see He et al., 2010). So what is this hullabaloo about? It appears it concerns itself over a newly discovered pinkie and there isn't much it can tell. You need more evidence than a pinkie to determine and describe a new species into an existing taxonomy. What Krause et al (2010) have found is a reconfirmation that hominid mtDNA is highly diverse. But yet, reading both Krause et al (2010) and the media, we are led to believe that a new species of hominid has been discovered. This is clearly not the case. Until further evidence is found (e.g., bones or bone fragments) and a diagnosis made can we be sure that “scientists have identified a previously unknown type of ancient human”.

References

Gauthier, J. A., Estes, R and de Queiroz, K 1988. A phylogenetic analysis of Lepidosauromorpha. In: R. Estes and G. Pregili (eds), Phylogenetic relationships of the lizard families. Stanford University Press, Stanford, CA, pp. 15-98.

He, Y., Wu, J., Dressman, D., Iacobuzio-Donahue, C., Markowitz, S., Velculescu, V., Diaz Jr, L., Kinzler, K., Vogelstein, B., & Papadopoulos, N. (2010). Heteroplasmic mitochondrial DNA mutations in normal and tumour cells Nature, 464 (7288), 610-614 DOI: 10.1038/nature08802

Krause, J., Fu, Q., Good, J., Viola, B., Shunkov, M., Derevianko, A., & Pääbo, S. (2010). The complete mitochondrial DNA genome of an unknown hominin from southern Siberia Nature DOI: 10.1038/nature08976